Being dependable and being available every second are two different jobs.

Dependable means what you said would happen, happens. Available means your phone gets answered within a minute. The two get treated as one virtue, which is unlucky, because only one of them has a limit. You can be the person everybody counts on and still be unreachable between nine and ten at night, and most people will never notice the difference.

Decide roughly how fast you answer things, then hold that instead of replying the second anything lands. Keep the promises exactly. Your reliability lives in the keeping, not in the speed of the reply.